1. Field of the Invention
The present invention relates to a method of manufacturing glass spacers and, more particularly, to a method of manufacturing glass spacers for electron beam-excited displays.
2. Prior Art
The conventional cathode ray tube (CRT) which is bulky and heavyweight has been replaced to an increasing extent by so-called flat panel displays which are thin and lightweight. The flat panel displays include liquid crystal displays. It is, however, expected that the liquid crystal displays will be replaced by light emitting type electron beam-excited displays, such as FEDs (Field Emission Displays) which generate fluorescence by irradiating an electron beam from an electron beam source on a fluorescent material or fluophor to thereby form images on the fluorescent material. Compared to the liquid crystal displays, these flat panel electron beam-excited displays provide images which are brighter and have a wider angle of view.
To form images through irradiation of the electron beam on the fluorescent material, however, the electron beam source, fluorescent material, and other components of the electron beam-excited display are necessarily incorporated in a vacuum casing under a vacuum atmosphere of the order of 10xe2x88x925 Torr or less. To support this kind of vacuum casing, an atmospheric pressure-resistant structure has been proposed, e.g. by Japanese Laid-Open Patent Publication (Kokai) No. 7-230776, which is described hereinbelow:
FIG. 1 is an exploded perspective view of the proposed flat panel electron beam-excited display. The flat panel electron beam-excited display in FIG. 1 is comprised of a face panel 1, which is formed of a glass plate 15 and an image forming member 5 deposited on the inner surface of the glass plate 15, and a back panel 2, on which a group of electron emitting devices, described later, are mounted. The image forming member 5 contains a fluorescent material or fluophor which emits light when irradiated with electron beams emitted from the electron emitting devices. The face panel 1 and the back panel 2 are joined together in an airtight manner by a support frame 3 as shown in FIG. 2, which is a cross-sectional view taken along line Axe2x80x94A in FIG. 1. The face panel 1, the back panel 2 and the support frame 3 define a hermetic atmospheric pressure-resistant structure. In addition, a plurality of glass spacers 4 are inserted between the face panel 1 and the back panel 2 as atmospheric pressure-resistant support members.
Each glass spacer 4 is formed of a tabular panel of a size of, for example, 0.2 mm in thickness and 5 mm in height. The glass spacer 4 is fixed at its lower end to the back panel 2 by a bonding material 8. Alternatively, the glass spacer 4 may be fixed at its upper end to the face panel 1 by the bonding material 8, or it may be fixed at its upper and lower ends to the face panel 1 and the back panel 2, respectively, by the bonding material 8.
The back panel 2 is comprised of a glass substrate 21, a multiplicity of element sections 23 arranged in a matrix array on the upper surface of the glass substrate 21, which are formed of nickel and have a thickness of 1000 angstroms, and a plurality of wiring sections 24 arranged on the upper surface of the glass substrate 21 to feed electric power to the element sections 23, which are formed of silver and have a thickness of 2 xcexcm. Each element section 23 has an electron emission element 25 formed thereon. The wiring sections 24 are arranged so as to provide a wiring pattern of parallel lines. Each pair of adjacent wiring sections 24 simultaneously feed electric power to a plurality of electron emitting devices 25 arranged along the wiring sections 24. Further, modulating electrodes, not shown, are arranged on the upper surface of the glass substrate 21 via a SiO2 insulating layer, which have electron passage holes of a diameter of 50 xcexcm at a location 10 xcexcm above the upper surface of the glass substrate 21.
Each glass spacer 4 is located relative to the back panel 2 such that the glass spacer 4 abuts on a wiring section 24 positioned between two rows of electron emitting devices 25 on the back panel 2. Each glass spacer 4 is located relative to the face panel 1 such that the glass spacer 4 abuts on a black stripe section of the image forming member 5, which is a portion of the fluorescent material not irradiated with the electrons emitted from the electron emitting devices 25.
Glass spacers 4 configured and arranged as above are manufactured by drawing a mother glass having a similar cross section to that of the glass spacer while heating the same to the softening point to obtain a drawn glass, and then cutting the obtained drawn glass into a suitable length, as disclosed, e.g. by Japanese Laid-Open Patent Publication (Kokai) No. 7-144939.
To produce such glass spacers by means of hot drawing with high precision, it is desirable that similarity in cross section between the mother glass and the drawn glass, specifically, the aspect ratio (height-to-thickness ratio) should be maintained to the maximum possible degree when producing the drawn glass by hot drawing the mother glass. If the similarity in cross section is maintained, it will be possible to obtain a glass spacer with a desired cross section by selecting a suitable cross section of mother glass.
In drawing the mother glass while heating the same to obtain a drawn glass, if the heating temperature is too high, the mother glass becomes too soft to maintain a desired similarity in cross section between the mother glass and the drawn glass, whereas, if the heating temperature is too low, the mother glass becomes too hard to draw and can be ruptured.
It is therefore an object of the present invention to provide a method of manufacturing glass spacers which can enhance the degree of similarity in cross section between the mother glass and the drawn glass when manufacturing glass spacers by hot drawing the mother glass.
To attain the above object, the present invention provides a method of manufacturing glass spacers, comprising the steps of preparing a mother glass having a similar cross section to a desired cross section of the glass spacer, and drawing the mother glass while heating the same to a viscosity of 105 to 109 poise.
Preferably, the mother glass is heated to a viscosity of 108 to 109 poise.
More preferably, the method of manufacturing glass spacers further comprises the step of feeding the mother glass at a predetermined feed speed while drawing the mother glass at a predetermined drawing speed, wherein the predetermined drawing speed and the predetermined feed speed are in a ratio of 20 to 4000.
In a preferred embodiment of the invention, the glass spacers are tabular and have a thickness of 0.03 to 0.25 mm.
Further, in a preferred embodiment of the invention, the glass spacers are tabular and have a height of 0.7 to 5.0 mm.
Further, the glass spacers are typically suitable for use in electron beam-excited displays.
The above and other objects, features and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.